GSM mobile phone networks use a signalling system to coordinate their operation. This signalling system is typically operated in accordance with the ITU Signalling System No. 7 (SS7) suite of protocols. It is known to monitor SS7 signalling messages traversing the signalling system in order to observe the operation of the network, and to obtain information about usage of the network's facilities. Such information is often collected in Call Detail Records (CDRs) (e.g. for voice calls) and Transaction Detail Records (TDRs) (e.g. for the use of other GSM services). For example SS7 ISDN User Part (ISUP) protocol messages are used to build CDRs to summarise voice service use, and SS7 Mobile Application Part (MAP) protocol messages, supported by the Transaction Capabilities Application Part (TCAP) protocol, are used to assemble summaries of messaging, mobility and access management activity.
To provide analogous functionality in GPRS networks, an additional transaction builder is required to summarise Internet Protocol (IP) service usage, for example of web browsing and e-mail services. The resulting transaction summaries are usually referred to as IP Data Records (IPDRs) or Service Usage Records (SURs). However, these transaction summaries are not normally built within the telecoms segment of the network (i.e. with access to ISUP and MAP messages) and therefore lack essential information that can only be obtained from these telecoms signalling transactions. For example, key information for billing and customer care includes the subscriber's International Mobile Subscriber Identity (IMSI) and the Mobile Station ISDN number (MSISDN). For monitoring Quality of Service (QoS) and network management the key fields are the GPRS Access Point Name (APN) and the negotiated QoS in the GPRS data access “tunnel” that is established using the GPRS Tunnelling Protocol (GTP, v0 defined in ETSI specification EN 301 347-GSM 09.60 and v1 defined in 3GPP specification TS 29.060). It is necessary therefore to be able to generate in an efficient manner SURs which include information obtained from a telecoms context.
One prior approach involves building IP SURs on the GPRS “Gi” interface. This is a pure computer data interface and carries no telecoms-related signalling messages that may be used to provide the desired information for the SURs. Therefore the separate GPRS “Gn” interface is monitored independently, to provide information on the GTP tunnel maintenance transactions in an entirely separate data feed. The SURs derived from messages on the Gi interface and the signalling transactions monitored on the Gn interface must then be correlated in an additional process in order to augment the SURs with telecoms context information. This approach requires the expense of monitoring equipment on both the Gn and Gi interfaces, additional transaction-building and correlation-computing capacity, and time to perform the correlation process.